Salicylic acid, explained

Salicylic acid is an exfoliant with one property that makes it different from every other one: it is oil-soluble. Glycolic and lactic acid are water-soluble, so they work on the surface of skin. Salicylic acid dissolves into sebum, which means it can get down inside a pore that is packed with oil and dead cells and break the plug up from the inside. That single chemical fact is why it is the default recommendation for blackheads, congestion and oily, acne-prone skin — and why it does comparatively little for the dry, sun-damaged surface texture that glycolic acid handles well.

What it is, and the BHA label

You will see salicylic acid called a BHA — a beta hydroxy acid — and the FDA notes it is by far the most commonly used BHA in cosmetics, appearing on labels as salicylic acid, salicylate, sodium salicylate or willow bark extract. A small honesty note the FDA itself makes: from a chemist's perspective salicylic acid is not strictly a beta hydroxy acid at all, but the cosmetic industry has called it one for so long that the label has stuck. Nothing about your buying decision changes because of this; it is simply the kind of detail we would rather you heard from us than discovered later.

The strengths that matter

• 0.5-1% — the gentle range, common in daily cleansers and toners. Suits sensitive or dry-but-congested skin, and is the right place to start if you have never used an acid.
• 2%— the workhorse, and the maximum concentration in over-the-counter acne products. This is what a leave-on liquid exfoliant like Paula's Choice uses, and it is where most of the visible results on blackheads happen.
• Above 2% — professional peel territory, not something to buy for home use. Higher is not better here; it is just more irritating.

Format matters as much as percentage. A 2% cleanser is on your skin for thirty seconds; a 2% leave-on liquid works for hours. If a 2% wash has done nothing for your congestion after a month, the answer is usually a leave-on at the same strength rather than a stronger wash.

What it does well

Blackheads and closed comedones are its home ground — it clears the plug rather than buffing the surface above it. It is mildly anti-inflammatory, which is why it calms the angry-looking bumps around a breakout rather than only the breakout itself. It reduces the look of enlarged pores, though the honest mechanism is emptying them rather than shrinking them; pore size is largely genetic. And it exfoliates the surface too, so skin looks brighter and feels smoother over a few weeks. For the products that use it well, see our acne roundup.

What it does not do

It does not treat hormonal cystic acne, which forms too deep for a topical exfoliant to reach — that is a conversation with a doctor, not a purchase. It does not shrink pores permanently. It does not replace a retinoid for texture and lines. And it is not a moisturizer; skin that is both congested and dehydrated needs salicylic acid and something with hyaluronic acid or ceramides in it, not one instead of the other.

The sun-sensitivity caveat, from the FDA

The Cosmetic Ingredient Review Expert Panel concluded that salicylic acid is safe as used in cosmetics when formulated to avoid irritation and to avoid increased sun sensitivity, adding that where sun sensitivity would be expected, directions for use should include daily sun protection. The FDA's own consumer precautions for BHA products are: patch-test on a small area first, stop if you get irritation or prolonged stinging, avoid using them on infants and children, and use sun protection. Government-run studies have determined that applying glycolic acid to skin increases susceptibility to sun damage including sunburn, and until the parallel salicylic acid work is complete the FDA advises treating both the same way. In practice: if you use salicylic acid, wear sunscreen daily. That is not a generic sign-off, it is the specific advice for this ingredient.

How to use it without wrecking your skin

1. Start twice a week, at night, on dry skin, and build up only if there is no stinging or flaking.
2. One exfoliant at a time. Salicylic acid plus glycolic acid plus a scrub is how people arrive at a raw, shiny, over-exfoliated face and blame the wrong product.
3. Separate it from your retinoid. Alternate nights. Both are irritants and stacking them is unnecessary.
4. Moisturize afterwards. Exfoliating without replacing lipids is half a routine — see our ceramides guide.
5. Give it six weeks. Congestion clears gradually. Judging it at ten days is how good products get abandoned.

Who should skip it

Anyone with a salicylate or aspirin allergy — salicylic acid is chemically related, and this is the one hard contraindication. Anyone whose skin is currently raw, peeling or reacting; fix the barrier first. And the FDA specifically advises against using BHA products on infants and children. If you are pregnant, the usual advice is that low-percentage topical salicylic acid is generally considered acceptable while oral and high-strength peel forms are not — but that is a question for your own doctor rather than a website.